1. Field of the Disclosure
The present disclosure relates generally to wireless communications systems, and more particularly, to a method and an apparatus for optimizing cell selection in a Dual Subscriber Identity Module (SIM) Dual Standby (DSDS) device.
2. Description of the Related Art
Mobile devices adapted for Multi SIM application are now becoming available to end users. A user benefit of such mobile devices is to be able to receive calls on several subscriptions using a single device. For example, a DSDS device is capable of receiving or sending messages associated with at least two subscriber identities. The two subscriber identities may be associated with the same or different cellular networks, and may use the same or different Radio Access Technologies (RAT). However, there is no network support for the Dual SIM design, hence it becomes a device's responsibility to ensure that the device achieves desired user experience.
In conventional Dual SIM configurations, one SIM (i.e., a First SIM) is in a connected mode (i.e., a Circuit Switched (CS) Call, Packet Switched (PS) Call, Voice over LTE (VOLTE), Voice over HSPA (VOHSPA)), and another SIM (i.e., a Second SIM) is configured to not perform any cell search or measurements and area update procedures. As a result thereof, a network to which the DSDS device belongs has no idea about a proximity of the DSDS device with respect to the second SIM, and eventually the DSDS device loses a context in a serving cell in an idle mode. Thus, the cell selection process can be delayed for the second SIM, which can cause the DSDS device to miss paging messages.
For example, when a CS call is ongoing on the first SIM, and due to a single Radio Frequency (RF) transceiver on the DSDS device, a cell search and measurement cannot be triggered on the second SIM. After CS call disconnection on the first SIM, the cell selection is triggered on the second SIM, thereby leading to a delay in camping onto the cell for the second SIM. Moreover, due to this delay, any paging for the second SIM is missed during the cell selection procedure on the second SIM as shown in FIG. 1A. Further, as shown in FIG. 1B, when the DSDS device is in the connected mode on the first SIM, the context of the second SIM is out of service. Thus, if the call ends on the first SIM, the second SIM initiates a network scan for recovering service on the second SIM, thereby rendering the second SIM unavailable to receive any paging messages and to gain service on the second SIM for a relatively long duration of time.
Moreover, in conventional systems and methods, there is an expected delay in the cell search on the second SIM. For example, after call disconnection on the first SIM, and due to delay in the cell search on the second SIM, the DSDS device can miss any immediate paging on the second SIM. In the DSDS device, after first SIM disconnection, if the stored cell search fails, a blind scan can be triggered, which will again be interrupted by a first SIM IDLE mode high priority operations, e.g., paging and cell reselection. Further, the mechanism for cell selection is sub-optimal, thus there is a potential to improve the cell selection.
The above information is presented herein as merely background information for helping the reader to understand the present invention. Applicants have made no determination and make no assertion as to whether any of the above might be applicable as Prior Art with regard to the present application.